1. Technical Field of the Invention
The invention relates to an optical pickup device, and more particularly to a device suitable for use in irradiating a recording medium having plural laminated recording layers with laser light.
2. Disclosure of Related Art
In recent years, as the capacity of an optical disc has been increased, an optical disc having an increased number of recording layers has been developed. Laminating recording layers in a disc enables to considerably increase the data capacity of the disc. In the case where recording layers are laminated, generally, two recording layers are laminated on one side of a disc. Recently, however, laminating three or more recording layers on one side of a disc has been put into practice to further increase the capacity of the disc. Thus, the capacity of a disc can be increased by increasing the number of recording layers to be laminated. However, as the number of recording layers to be laminated is increased, the distance between the recording layers is decreased, and signal deterioration resulting from an interlayer crosstalk is increased.
As the number of recording layers to be laminated is increased, reflection light from a recording layer (a targeted recording layer) to be recorded/reproduced is reduced. As a result, if unwanted reflection light (stray light) is entered into a photodetector from a recording layer on or under the targeted recording layer, a detection signal may be deteriorated, which may adversely affect focus servo control and tracking servo control. In view of this, in the case where a large number of recording layers are laminated, it is necessary to properly remove stray light, and stabilize a signal from a photodetector.
Further, an optical pickup device is required to have compatibility with Compact Disc (CD) and Digital Versatile Disc (DVD), Blu-ray Disc (BD). Among the discs, BD has a narrower interval between recording layers than that of the other discs, and the number of recording layers included in one disc of BD is larger than that of the other discs. In view of this, particularly, there is an increasing demand for effectively eliminating an influence by stray light in BD.
On the other hand, the technology relating to the optical pickup device for CD and DVD has already been accumulated. Accordingly, it may be desirable to simplify the optical system and the sensor layout of the photodetector by applying the existing technology to CD and DVD as it is, rather than suppressing stray light.
However, it is necessary to modify the sensor layout of the photodetector, in the case where laser light for CD, laser light for DVD and laser light for BD are received by a single photodetector. In particular, in the case where an arrangement by an existing 3-beam system is applied to CD and DVD, it is necessary to efficiently arrange sensors for receiving laser light of each wavelength because the number of sensors on the photodetector is increased.